It's possible that "you are not the target market"; i.e. the fat part of the market demographic does have "100 or fewer" books on the device, and so the devices cater to that part of the market first.

But I agree, the search facilities in almost all the e-reading software I've seen leaves a lot to be desired (sort of like assuring all novelists that of course they can write their books using notepad or textedit or vi).